In the Golarion setting, apostasy wraiths (statted up by Greg Vaughan) are the souls of Razmir’s faithful, seeking revenge on the false god’s priests for leading them astray. They also hate all other religious leaders out of jealousy and shame for having been duped. And since even in death these souls are reluctant to attack Razmir’s priests, it’s often the true priests who paradoxically suffer most from the wraiths.
Of course, your campaign may not have Razmir, but any similar false faith will do. Apostasy wraiths are particularly common near dragon and aberration cults, for instance. Other strong codes, including monastic vows or the creeds of knighthood, might also inspire the creation of these wraiths. All that is needed is for the belief to be fervent enough...and the betrayal, once revealed, to be truly soul-shattering.
Adventurers enter the Forbidden Kingdom of Tyrparthax the Winged God, a mighty red dragon. There half-dragons and dragon-blooded sorcerers serve as priests for the faith Tyrparthax believes will elevate him into a nascent deity. The adventurers also discover most major cities in Tyrparthax have rather strict curfews. This is not the Winged God’s doing, but his false priests’—because all of these cities have problems with apostasy wraiths after dark.
Con man Reginald Barstow has been a forger, a gold dowser, a spiritualist, and even masqueraded as a reborn god. This last scam got him into more than the usual amount of trouble when the authorities raided his storefront church and several cultists wound up dead. Now one of them follows him as an apostasy wraith—still too in awe of him to attack, but haunting Barstow incessantly and making future scams impossible. He’s willing to offer a number of illicit services to the adventuring party that can permanently drive away the vengeful shade.
Apostates in drow communities face an uncertain afterlife. Raised to believe that their city-state’s deity—the Matron of Spiders, the Scorpion Goddess, the Locust Queen, and so on—is the only true goddess in existence, those few who renounce their faiths expect no eternal reward. An apostate soul’s discovery of whole other pantheons is a traumatic one, and they often return to the mortal world as apostasy wraiths, lurking near border caverns or in the shadows of the great drow fanes to punish those priests who denied them a full religious existence.
—Inner Sea Bestiary 4
Of course, for the best apostate ever you need to be reading Daniel Abraham’s The Dagger and the Coin Quintet.
Daily Planescape also took a crack at the apostasy wraith. Check it out here.
Are any of you at PaizoCon? Let us know how it is. I was hoping to go but life got in the way—this is the first time my entire family has been able to get together in about 3 to 5 years, so that had to come first. (That is why I am in MA, where it is so humid thanks to Hurricane Arthur that my Pathfinder softcovers are literally curling into sine waves.)